Panasonic EB-X300 - Manual (Page 99)

96 Phone Menu
SIM lock
Once you enable the SIM lock, you will be prompted to enter
your phonecode when you switch on the phone with a different
SIM inserted.
From Phone Menu
1.
4 Security A (Select)
2. 4 SIM lock A (Select)
3. Enter the phonecode A (OK)
4. A (Change) to set the SIM lock on/off
5. @ (OK)
NOTE: Your phonecode must be 6 to 12 digits. You are advised to
write down your phonecode. If the phonecode is entered incorrectly
10 times, the phone will cease to operate permanently. If you change
the phonecode from the second time on, you must enter the previous
phonecode first, then enter the new phonecode twice.
NOTE: This function is SIM dependent.